Geophysical signatures of South Australian mineral deposits: Miscellaneous and minor deposits

Abstract

Mississippi Valley-type lead-silver mineralisation at Ediacara is associated with IP/resistivity anomalies, although there is a strong possibility the mineralisation itself is not responsible for the response. There are no anomalous responses on ground magnetic and frequency-domain electromagnetic data. At the Telephone Dam lead-zinc sulphide deposit ground magnetic surveys only poorly defined the host stratigraphy. Electromagnetic surveys were hindered by the conductive overburden, and bedrock responses that were obtained were found to be due to graphite and barren sulphide mineralisation. Lateritic nickel mineralisation at Claude Hills is associated with negative gravity anomalies, but variations in the depth of weathering cause similar responses. Massive pitchblende mineralisation at Myponga gives rise to anomalous responses in Geiger counter and airborne radiometric surveys. However, pegmatites in the region also give rise to anomalous radiometric responses. Gravity surveys at the Yanyarrie barite deposit successfully defined positive anomalies associated with mineralisation. Hydrothermal copper-molybdenum mineralisation at Anabama Hill may be of porphyry-type. Airborne and ground magnetic surveys define a positive anomaly surrounded by an annular negative anomaly. This may be associated with concentric zones of alteration. Resistivity surveys detected areas of altered granite and shear zones, whilst surface and downhole IP measurements had some success at detecting sulphides. Electrical and electromagnetic surveys within the Teetulpa Goldfield were unsuitable for locating sulphides in bedrock. However, seismic refraction surveys successfully mapped the geometry, but not the internal stratigraphy, of palaeochannels prospective for alluvial gold. At the Acropolis prospect, located in the basement to the Stuart Shelf, copper, uranium and rare-earth-element mineralisation is closely associated with large bodies of haematite-magnetite alteration. At the nearby Wirrda Well prospect copper, and to a lesser extent uranium and gold, mineralisation occurs within altered granitic breccias. Both areas are associated with high-amplitude positive gravity and magnetic anomalies.